Many musicians now prefer vacuum tube preamplifiers and particularly those which can provide, as desired, linear or clean undistorted amplification or amplification which is non-linear or distorted with desired amounts of harmonic content. In part, it is believed that having a controlled amount of distortion when desired provides amplified sound that is more pleasing to the human ear and has a richer, fuller tone. As only particular passages of music are to be reproduced with non-linear or distorted sound characteristics, amplifiers which can be alternately operated in distorted and undistorted modes have been developed.
This has been accomplished in several ways such as using extra amplification stages or a different set of amplification stages to provide a distorted signal. In such arrangements there will be amplification stages which are not used in every mode of operation. As even clean undistorted music signals can benefit from having more amplification stages over the minimum needed for voltage gain it would be advantageous and efficient to have musical instrument amplifiers having multiple stages and having various modes of operation, some of which provide distortion, which use all of the stages of the amplifier in all modes of operation.